Digging a well and installing a communal hand pump costs $1,700 a year over ten years. This cost can be spread around the 300 people it would help. It would save each household more than three hours a day in water collection time, and reduce the incidence of diarrhoea by about 30%.

Making new loans averaging $285 to 348,000 poor borrowers would increase their household consumption in the first year by 9.45% and have a positive effect on spending for a further two generations.

A high-quality outcome to the Doha Round would increase global income by more than $3000 billion per year, four-fifths of which would go to today’s developing countries. Adjustment costs for some players in the global market would cost up to $71 billion per year.

Spending US$1b on malaria prevention and treatment each year would save 500,000 deaths – most of them in children. Benefits include a lower burden on the health system.

Boosting children’s’ health would cost as little as $3.50 per year per child (as a Kenyan de-worming program did, which increased the total average time spent in school by nearly two months) or as much as $1,394 (like a nutritional program in Bolivia that permanently improved cognitive development and motor skills).

For $2.3b we could provide a chimneyless rocket stove to half the people using unhealthy, old-fashioned stoves. This would cut the negative health effects caused by solid fuel use by a third. Solid fuel use causes 1.5m deaths each year.

Migration from poor countries increasing the richest 30 nations’ workforce by three percent by 2025 would cost up to $21,000 per migrant in the year of migration, shared equally by migrants and host governments, and bring overall economic benefits of up to $38 trillion.

Providing Vitamin A and Zinc supplements to 80% of children under-two across Sub-Saharan Africa and South Asia for a year would require just US$60m. Benefits from improved future earnings and reduced healthcare spending would add up to US$240m each year.

Developing community-based education programs (rather than supplying supplements) could lead to lasting dietary improvements. Spending US$798m would develop programs for 80% of the worst-affected families with young children in affected areas, and potentially lead to annual benefits from a reduced burden on the healthcare system and healthier population of US$10 billion.

Providing a filter that ensures clean drinking water would cost just US$100 per household up front, including transport and delivery, and reduce diarrhoea by around 40%.

A total of $800b spent on both accelerating the phase-in of carbon-extensive energy technologies and on mitigation (use of carbon taxes) would slow warming by about 0.5 degrees Celsius by 2100.

Heart disease represents more than a quarter of the death toll in poor countries. Developed nations treat acute heart attacks with inexpensive drugs that aren’t available in the developing world. Spending just $200 million getting these cheap drugs to poor countries would avert 300,000 deaths in a year. The benefits come from improved health and productivity, as well as a lower burden on the health system.

Spending between $15 and $20b a year targeting terrorists proactively could reduce the number of attacks by 50 (or 13%) a year but this would not decrease the death-toll or injury rate because terrorists would resort to more violent attacks in response to the higher risks.

In India, village councils with quotas for women village chiefs have higher levels of safe drinking water, better immunization coverage and roads, and less bribery. There may be some losses from electing women because they tend to have less experience in politics than men, but the Indian experience suggests that if it took twenty years to establish a 30% share of women in local positions, the benefits would at the very least double the costs of achieving this.

Creating a financial incentive for drop-out students to return to school would cost between $150 and $2,500 a year per child, depending on the program. It would increase enrolment rates, particularly in poor, rural areas. Each extra year of schooling increases future earnings by an average of 8%.

Spending US$850m on a peacekeeping force in each of the first five years after a conflict (and less after that) reduces the risk a country will return to violence by more than 30%. Averting conflict leads to significant economic benefits to the nation, its neighbours and other countries.

Improving the ability to financially monitor and trace terrorists’ funds would cost about US$128 million annually and prevent one spectacular terrorist event per year, on a scale similar to the August 2006 plot against trans-Atlantic flights.

Lifting growth by 1 percentage point reduces by 1.5 percentage points the risk of conflict re-emerging. Achieving a 1 percentage point lift in GDP typically requires annual aid of US$400m.

Diesel vehicles are a significant contributor to urban pollution. In China alone some 400,000 people die annually due to exposure to this pollution. Pollution control technology for vehicles remains expensive, so the cost/benefit ratio is low.

Spending a total of $800b introducing carbon taxes of around $20 per ton of CO2 would slow global warming by about 0.2 degrees Celsius by 2100.